Recent pneumatic tires are required to have various kinds of enhanced performance, and their tread patterns are contrived to enhance the performance. Heavy duty tires are provided with tread patterns that enhance traction performance.
For example, a heavy duty pneumatic tire is known that improves in both traction performance in traveling on a bad road and wet performance in traveling at high speed until the terminal stage of wear (Japanese Unexamined Patent Application Publication No. H09-136514A). The heavy duty pneumatic tire includes, in a tread, at least one circumferential groove extending in the circumferential direction and a large number of lateral grooves connecting with the circumferential groove and disposed on both sides of the circumferential groove while separated from each other in the circumferential direction. In the pneumatic tire:
(1) the circumferential groove extends in the circumferential direction in a tread central region that corresponds to 50% of the tread width;
(2) the depth of the circumferential groove is 5% of the tread width or greater; and
(3) the depth of at least lateral grooves disposed in both side sections of the tread among the lateral grooves is 109% of the depth of the circumferential groove or greater.
According to Japanese Unexamined Patent Application Publication No. H09-136514A, this configuration enhances both traction performance in traveling on a bad road and wet performance in traveling at high speed.
In heavy duty pneumatic tires, land portions in the tread central regions have areas increased for improving cut resistance and wear resistance. Such a land portion in the tread central region having an increased area decreases a groove area and thus decreases edges, causing a reduction in traction performance.
The heavy duty pneumatic tire according to Japanese Unexamined Patent Application Publication No. H09-136514A can improve in traction performance in the terminal stage of wear; however, the tread central region is worn earlier than the tread shoulder regions before the terminal stage of wear.
Especially pneumatic tires that are fitted to buses, trucks, or the like, or large tires that have a size of, for example, 49 inches or greater and are fitted to dump trucks traveling off-road, for example, on mines are preferred to improve in both traction performance and wear resistance in the tread central regions in view of effective use of the tires.